Sensory/Perceptual Problems

Aging affects sensory and perceptual capabilities. Commonly affected are:

• Vision
• Depth perception
• Visual attention

Vision

Vision is the primary sense used in driving. About 90 percent of the information required for driving safety relates to vision. Normal aging affects a number of eye functions key to seeing objects on and near the roadway. Many older adults can or have adapted their driving when they recognize these normal changes. Regular vision checkups are vital for maintaining good vision and correcting problems as they arise.²⁸

Depth Perception

Depth perception is the ability to determine the distance of objects. With age, changes in the eye's lens decrease the ability to accurately determine distances between two objects. Older drivers tend to use the distance of the approaching vehicle, rather than its speed, to determine safe turning, changing lanes, or merging.²⁹ By miscalculating speed, older adults may inappropriately turn or pull out into traffic, resulting in a near miss or crash.

Useful Field of View

The "useful field of view" refers to the area that one can see and cognitively process and interpret.³⁰ With cognitive slowing, the area shrinks to only the area a person sees directly in front of the eyes without the side vision, called peripheral vision. Drivers with decreased visual attention can only see the car directly in front and not the pedestrian stepping from the curb. Drivers can adapt to reduced useful field of vision through retraining by an occupational therapist.

Contrast Sensitivity

The capacity to sharply see the difference between two similarly colored objects indicates the ability to perceive contrast. With age, older adults may develop cataracts, which change perception of color and background. When driving, the inability to see the difference in contrast affects distance judgment. Drivers may have difficulty determining the distance of an object, resulting in "tailgating" or hitting a curb. Other examples include the ability to see objects lying in the road that are a similar color to the pavement, faded highway lane makers, or pedestrians in dark clothing at night.

Perceptual Reaction Time (PRT)

This refers to the speed with which the driver can process visual information. As one ages, this interaction between the eye and the brain's ability to recognize what it sees is reduced. Good PRT is critical to seeing hazards and recognizing warning signs in a timely manner.³¹

Glare Recovery

Glare occurs when:

1. Brightness of an object approaches us faster than our eyes can accommodate, or
2. The eye's ability to focus incoming light diminishes.

With age the eye's lens hardens thereby increasing the amount of "stray" light entering the eye. This light scatters, causing the appearance of "dazzling bright spots." Resistance to glare declines by 50 percent every 12 years after age 40.³² Time needed to recover from glare also increases with age. Glare affects driving by momentarily blinding the driver. Glare from oncoming headlights at night requires quick recovery to maintain the car's appropriate course.

Peripheral Vision

Peripheral vision is the ability to see objects to the side when the eyes are focused forward. With age, the range of side vision decreases.

For example, many older people have reported that, all of a sudden, a car whizzed past or a vehicle from another lane pulled in front of them. Reduced peripheral vision results in "blind spots," or areas in the car from which it is difficult to see objects. Adaptive equipment and retraining can improve the driver's ability to overcome blind spots.

Light/Dark Adaptation

Light and dark adaptation is the ease with which the eye can adjust to changes from dark or dim lighting to bright areas. Adaptation diminishes with age as the eye muscles become less elastic. For example, many older drivers have difficulty seeing when entering or leaving a tunnel.

Conditions that affect vision and appear more frequently with age include, but are not limited to, cataracts, glaucoma, and macular degeneration.

Vision Conditions Affecting Driving³²
(For a definition of the conditions in the following tables, see the glossary of this module)

²⁸ American Medical Association (Nov. 21, 2002) "Why are older drivers at risk?" Retrieved from the AMA on the World Wide Web: www.ama-assn.org/ama/pub/category/9115.html.

²⁹ NHTSA, "Depth Perception." Older Road User Research Plan.

³⁰ Ibid., "Visual Attention."

³¹ Hennessy, D. (1995) "Crashes Predicted when Compensation for Visual Impairment Is Inadequate." Research Notes. Retrieved from California Department of Motor Vehicles on the World Wide Web: www.dmv.ca.gov/about/profile/rd/resnotes/crashes.htm

³² Hogan, D.B. (1999) "The Older Driver." Retrieved from Calgary University Faculty of Medicine on the World Wide Web: www.med.ucalgary.ca/oemweb/elderdrivers/dementia.htm.

³³ The information in these tables is adapted from the following source unless otherwise cited. NHTSA, Safe Mobility for Older People Notebook, pp. 3-29.

³⁴ MEDLINEplus. Medical Encyclopedia "Cataracts." Retrieved from National Library of Medicine on the World Wide Web: www.nlm.nih.gov/medlineplus/ency/article/001001.htm.

³⁵ Ibid.

³⁶ Owsley, C, et al. (2002) "Impact of cataract surgery on motor vehicle crash involvement by older adults." Journal of the American Medical Association 288:841-49.

³⁷ National Eye Institute. "Facts About Glaucoma." Retrieved from NEI on the World Wide Web: www.nei.nih.gov/health/glaucoma/glaucoma_facts.htm.

³⁸ MEDLINEplus. Medical Encyclopedia "Glaucoma." Retrieved from National Library of Medicine on the World Wide Web: www.nlm.nih.gov/medlineplus/ency/article/001620.htm#Causes,%20incidence,%20and%20risk%20factors.